"The Iranian government has never explained why Jason was detained or why he has been held for more than four months without access to a lawyer,” Baron said.

He added that Rezaian was acting as a “fully accredited journalist."

Rezaian, 38, has been the “Washington Post’s” bureau chief in Tehran since 2012.

U.S. Secretary of State John Kerry called on the Iranian government to drop any and all charges against Rezaian and release him immediately, saying he poses no threat to Iran’s government or to the country's national security.

Kerry said in a statement issued early on December 7 that the United States shares the concerns of Rezaian’s family regarding reports that he is under physical and psychological distress, and is not receiving proper medical care.